1. Field of the Invention
The present invention relates to an improvement on a position control apparatus, a focus adjustment apparatus and a camera, for controlling the position of a moving member.
2. Description of Related Art
As methods for controlling the position of a lens barrel, there is known, as disclosed in Japanese Laid-Open Patent Application No. HEI 8-122617, a mechanism arranged such that a reference position of a lens barrel in the optical axis direction is decided by a discrimination means which is arranged to decide one reference position and, after that, an extent to which the lens barrel is to be drawn out is controlled by reading, with a photo-interrupter, the rotating position of a pulse plate (disk) provided on the shaft of a motor.
Some of cameras having zoom lenses are arranged to vary a photo-taking magnification by varying the positions of at least two lens groups in the optical axis direction. It is known that, in a camera of this kind, a drive source such as a stepping motor is arranged integrally with a first lens group to be capable of driving and moving a second lens group in the optical axis direction, the position of the second lens group in the optical axis direction is computed and obtained from information on the focal length of the photo-taking lens and information on a distance to an object to be photographed, and the second lens group is controlled and driven by the drive source to the computed position. A photo-taking lens barrel arranged in this manner obviates the necessity of a conventional mechanism called a mechanical cam mechanism which is arranged to control lens positions in the optical axis direction by means of cam grooves formed in a cam tube and rectilinear motion guide grooves formed in a rectilinear motion guide tube.
Generally, the structural arrangement described above is called an electronic zoom mechanism. In brief, the electronic zoom mechanism is arranged as follows.
Information on the focal length varied by a magnification varying action on the photo-taking lens is detected by a known position detecting means. A distance to the object to be photographed is detected by a known distance detecting means. The position of the second lens group relative to the first lens group necessary for focusing on the object is decided by these processes. The first lens group is provided with a detector for detecting the position of a part which is arranged at the second lens group to be detected by the detector. When a shutter release operation is performed by the camera user, the second lens group is driven to the position decided in relation to the first lens group on the basis of a detection signal of the detector.